The present disclosure relates to spatial light modulators.
In general, a spatial light modulator (SLM) includes an array of cells, each of which includes a micro mirror that can be tilted about an axis and, furthermore, circuitry for generating electrostatic forces that operate to tilt the micro mirror. In addition, a cell typically includes structures that hold and allow the tilting of the micro mirror. In conventional SLMs, there are gaps between cells for accommodating such structures. The cell usually further includes a first structure and a second structure configured to mechanically stop the cell's micro mirror at the “on” position and the “off” position, respectively. These structures are referred to as mechanical stops.
In one implementation, for example, a digital mode of operation for displaying video images, there are two positions at which the micro mirror can be tilted. In an “on” position or state, the micro mirror directs incident light to an assigned pixel of a display. In an “off” position or state, the micro mirror directs incident light away from the assigned pixel. The “on” position can be, for example, 20 degrees from the horizontal in a first direction of rotation about the axis, and the “off” position can be, for example, 15 degrees from the horizontal in the opposite direction.
An SLM implemented as described above generally operates by tilting a selected combination of micro mirrors to selectively project light to display an image on the display. A display that implements SLM technology is typically required to refresh images at high frequencies typical of video applications. Each instant of refreshing can include changing the state of all or some of the micro mirrors. Providing a fast response by the micro mirrors therefore can be crucial to the proper operation of an SLM-based display device. One issue with response time is related to the stiction, i.e., surface contact adhesion, between the lower surface of the mirror and the mechanical stop in contact with the surface. Stiction can cause a delay in the mirror's response or may even prevent the mirror from changing state.